1. Field of the Invention
The present invention relates to a cuff for a blood pressure monitor provided with a fluid bag for avascularization of an artery by pressing a living body, and a blood pressure monitor having the cuff.
2. Description of the Background Art
To measure a blood pressure value, generally, a cuff provided with a fluid bag for pressing an artery located within a living body is wound around the body surface, and arterial pressure pulse waves caused in the artery by inflation/deflation of the fluid bag are detected to measure the blood pressure value. Here, the cuff refers to a band-shaped structure having a bladder, which can be wound around a part of a living body, for use in measurement of arterial pressure of an upper limb, a lower limb or the like by introducing fluid such as gas or liquid into the bladder. Thus, the cuff represents the concept including the fluid bag as well as members for winding the fluid bag around the living body. Particularly, the cuff wound around and fitted on a wrist or an upper arm is also called an arm band or a manchette.
Recently, blood pressure monitors are often used not only in medical treatment facilities such as hospitals but also in the households as an apparatus for checking the physical conditions day by day. As such, there are strong demands for improvement in handling of the blood pressure monitors, particularly for ease in fitting operation. To this end, downsizing of the cuff has been attempted. To downsize the cuff, it is necessary to narrow the cuff particularly in the width direction (i.e., direction parallel to the axial direction of the measurement site (e.g., wrist, upper arm or the like) to which the cuff is applied), for achievement of excellent fitting even for a person having an upper arm of short length, or for improved fitting to a wrist.
To narrow the width of the cuff for the blood pressure monitor, it is important to ensure that the artery is sufficiently pressed for avascularization. In the case of using a cuff for a blood pressure monitor having a large width, a long length in the axial direction of the measurement site covered by the cuff can be guaranteed, which enables sufficient pressing and avascularization of the-artery. However, if the width of the cuff is narrowed, the length in the axial direction of the measurement site covered by the cuff becomes short, in which case it would be difficult to sufficiently press the artery for avascularization. This will be explained in detail in the following.
FIGS. 12A-12C are conceptual diagrams illustrating avascularization performance in the case where a cuff for a blood pressure monitor of Conventional Example 1 is used to press the artery inside the living body for avascularization. FIG. 12A is a schematic cross sectional view in the width direction of the cuff for a blood pressure monitor of Conventional Example 1, showing the state where the cuff is fitted on the living body. FIG. 12B is a schematic cross sectional view showing the state where the artery is pressed for avascularization using the cuff for a blood pressure monitor of Conventional Example 1. FIG. 12C shows pressure distribution over the surface of the living body when pressed with the cuff for a blood pressure monitor of Conventional Example 1. In FIGS. 12A and 12B, the cover body covering the air bag is not shown.
As shown in FIG. 12A, the cuff 130D for a blood pressure monitor of Conventional Example 1 includes an air bag 150D formed by laying two resin sheets 151 and 152 one on the other and melting and bonding their rims, and a curled elastic member 160 identified as an elastic member that is attached to an outer peripheral surface of air bag 150D using a double-faced tape 171 identified as an attaching member. Air bag 150D has an inflated/deflated space 157 therein, and has a bonded portion 156 on each end in the width direction that is formed by the above-described melting and bonding. In the fitted state of the cuff, air bag 150D is located between the surface of living body 300 and curled elastic member 160. Herein, the width of air bag 150D is represented as L1.
When a pressurized air is introduced into inflated/deflated space 157 to inflate air bag 150D, air bag 150D increases in size in the thickness direction, as shown in FIG. 12B, and its working face 158 pressing living body 300 expands in a balloon shape. With curled elastic member 160 secured, inflation of air bag 150D outwards, i.e., in the opposite direction from living body 300 is restricted, and air bag 150D is inflated only on the side of living body 300. As such, living body 300 is pressed by air bag 150D, and the artery 301 located under the skin of living body 300 is pressed for avascularization.
In order to completely occlude artery 301, it is required that the pressure applied by air bag 150D to the surface of living body 300 is not less than a prescribed level. That is, when the pressure on the surface of living body 300 required to completely occlude artery 301 is represented as PA, artery 301 is occluded only in the region where the pressure distribution curve 200 on the body surface exceeds pressure PA, as shown in FIG. 12C. Herein, the length or distance of a portion of artery 301 in its extending direction occluded by inflation of air bag 150D (hereinafter, referred to as “artery occluded distance”) is represented as L2.
In the state where artery 301 is pressed for avascularization, a pressure P2 within artery 301 on its central side represents a blood pressure value. In the blood pressure monitor, a change of pressure P1 within air bag 150D is read as pressure P2 on the central side within artery 301, to calculate the blood pressure value. Thus, for accurate measurement of the blood pressure value, it is necessary to minimize the difference between pressure P2 within artery 301 and pressure P1 within air bag 150D to the greatest possible extent, for which it is critical to secure a sufficiently long length of artery occluded distance L2 described above.
With the configuration of air bag 150D arranged inside cuff 130D for a blood pressure monitor of Conventional Example 1, however, air bag 150D is inflated in the balloon shape, making it difficult to sufficiently guarantee artery occluded distance L2 with respect to width L1 of air bag 150D. This causes degradation of accuracy in measurement, which problem is particularly noticeable when width L1 of cuff 130D for a blood pressure monitor is decreased. Such degradation of measurement accuracy due to deterioration of avascularization-performance poses a very serious problem.
A cuff for a blood pressure monitor disclosed in Japanese Patent Laying-Open No. 02-107226 and a cuff for a blood pressure monitor disclosed in Japanese Patent Laying-Open No. 2001-224558, for example, are known as those directed to prevent degradation of avascularization performance in association with a decreased cuff width. In each of the cuffs for a blood pressure monitor disclosed in these publications, an air bag identified as a fluid bag arranged inside the cuff is provided with a gusset at each end in the width direction. When the air bag is inflated, the gussets expand to make the air bag inflated more uniformly in the width direction. Particularly in the case where the configuration disclosed in Japanese Patent Laying-Open No. 2001-224558 is employed, artery occluded distance L2 of a very long length can be guaranteed with respect to the width of the air bag, thereby rendering this technique essential for reduction of the cuff width. Hereinafter, the cuff for a blood pressure monitor disclosed in Japanese Patent Laying-Open No. 2001-224558 will be explained as Conventional Example 2.
FIGS. 13A-13C are conceptual diagrams illustrating avascularization performance when using the cuff for a blood pressure monitor of Conventional Example 2 to press the artery inside the living body for avascularization. FIG. 13A is a schematic cross sectional view in the width direction of the cuff for a blood pressure monitor of Conventional Example 2, showing the state where the cuff is fitted on the living body. FIG. 13B is a schematic cross sectional view showing the state where the artery is pressed for avascularization using the cuff for a blood pressure monitor of Conventional Example 2. FIG. 13C shows pressure distribution over the surface of the living body when pressed with the cuff for a blood pressure monitor of Conventional Example 2. In FIGS. 13A and 13B, the cover body covering the air bag is not shown.
As shown in FIG. 13A, the cuff 130E for a blood pressure monitor of Conventional Example 2 includes an air bag 150E and a curled elastic member 160. Air bag 150E has a bag member formed by laying two resin sheets 151 and 152 one on the other and melting and bonding their rims, and another bag member formed by laying two resin sheets 153 and 154 one on the other and melting and bonding their rims, which bag members are laid one on the other and melted and bonded together to form air bag 150E. Curled elastic member 160 identified as an elastic member is attached to an outer periphery surface of air bag 150E using a double-faced tape 171 as an attaching member. Air bag 150E has two layers of inflated/deflated spaces 157a, 157b therein, which are in communication with each other via a communication hole 159. Bonded portions 156a1, 156a2, formed by the above-described melting and bonding, are located at each end in the width direction of air bag 150E. In the fitted state of the cuff, air bag 150E is arranged between the surface of living body 300 and curled elastic member 160.
When a pressurized air is introduced into inflated/deflated spaces 157a, 157b to inflate air bag 150E, air bag 150E increases in size in the thickness direction, as shown in FIG. 13B. Since the gussets are provided at the respective ends in the width direction of air bag 150E, they expand in the thickness direction of air bag 150E, whereby a working face 158 of air bag 150E pressing living body 300 expands approximately flatly. As such, the both ends in the width direction of air bag 150E and their vicinities expand similarly to the central portion in the width direction of air bag 150E, ensuring more uniform pressing of artery 301 under the skin of living body 300.
As described above, with the configuration of air bag 150E contained in cuff 130E for a blood pressure monitor of Conventional Example 2, working face 158 of air bag 150E pressing the living body expands approximately flatly. Thus, compared to the case of air bag 150D contained in cuff 130D for a blood pressure monitor of Conventional Example 1, artery occluded distance L2 can be secured longer with respect to width L1 of the air bag. As a result, it is possible to measure a blood pressure value with accuracy even if the cuff width is reduced.
Although the structure of air bag 150E contained in cuff 130E for a blood pressure monitor of Conventional Example 2 is suitable for accurate measurement of the blood pressure value, it requires a large number of resin sheets, and also requires joining of the resin sheets in several steps. As such, the production is complicated, and the cost is high.